The invention relates to an eccentric screw pump, also known as a “helical gear pump”, in particular for conveying viscous, highly viscous and abrasive media, having a longitudinal direction L, exhibiting at least one conical, helically wound, at least single-start rotor having a pitch h, having at least one eccentricity e and at least one cross-section d that is rotatably arranged in a single or multi-start conical stator. A plurality of chambers, each having a volume formed between the rotor and the stator, serve to convey the medium. These chambers between the stator and the rotor are delimited by a sealing line D. Furthermore, the invention relates to an eccentric screw pump, in particular for conveying viscous, highly viscous and abrasive media, having a longitudinal direction L, exhibiting at least one stepped, helically wound, at least single-start rotor having a pitch h, having at least one eccentricity e and at least one cross-section d that is rotatably arranged in a single or multi-start stepped stator.
Eccentric screw (helical gear) pumps are quite well known in the art. The German Patent No. DE 633,784 describes an eccentric screw pump in which two helical elements are intertwined. The outer element has one more worm threads or teeth than the inner element and the pitches of the worm threads of the two elements behave like the thread or tooth numbers, that, however, can be either constant, increasing or decreasing. At least three interacting spiral-shaped elements are provided, of which the middle one has one tooth more than the inner one and one tooth less than the outer one.
Known from the German Patent Publication No. DE 27 36 590 A1 is an eccentric screw pump with a conical screw shaft and a housing insert, which is characterized by the fact that the eccentric screw shaft has a round, cylindrical base cross-section and a conically increasing tapered outer diameter. The conically wound, inner hollow screw with twice the pitch of the eccentric screw shaft causes a tapered hypocycloidal rolling off on the eccentric screw shaft on the inside surface of the conical, wound hollow screw.
The problem with eccentric screw pumps of the prior art that have multiple chambers is that so-called “cavitations” may occur, caused by increases in the chamber volume due to wear, with the result that the conveying capacity of such eccentric screw pumps does not remain optimal.